import java.util.Arrays;
import java.util.Scanner;

public class demo1 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int w=scanner.nextInt();
        int h=scanner.nextInt();
        boolean[][] arr=new boolean[w][h];
        for(int i=0;i<w;i++) {
            Arrays.fill(arr[i], true);
        }
        int count=0;
        for(int i = 0;i<w;i++) {
            for(int j=0;j<h;j++) {
                if(arr[i][j]==true) {
                   count++;
                   if(i+2<w) {
                       arr[i+2][j]=false;
                   }
                   if(j+2<h) {
                       arr[i][j+2]=false;
                   }
                }
            }
        }
        System.out.println(count);
    }
}
